Getter structure for electrical discharge and method of making the same

ABSTRACT

A nonevaporating getter, which is optionally heatable in operation within an electron discharge vessel, in which the getter material contains at least one metal selected from the group consisting of Zr, Ta, Hf, Nb, Ti, Th and U, and is disposed directly on the insulating layer of the heating means, eliminating the use of an open metal vessel or the like for the getter material.

United States Patent Inventor Manfred Wintzer Munich, Germany Appl, No.810,743 Filed Mar. 26, 1969 Patented June 8, 197 l Assignee SiemensAktiengesellschaft Berlin and Munich, Germany Priority Apr. 1, 1968Germany P 17 64 092.5

GETTER STRUCTURE FOR ELECTRICAL DISCHARGE AND METHOD OF MAKING THE SAME3 Claims, 1 Drawing Fig.

US. Cl 313/180, 252/18l.6,4l7/51 Int. Cl H0lj 19/10 Field of Search 3 l3/174,

[56] References Cited UNITED STATES PATENTS 1,958,967 5/1934 Kniepen313/178X 2,175,695 10/1939 Kniepen 252/181.6X 2,855,368 10/1958 Perdijket al... 252/1816 3,102,633 9/1963 Baronetzky 206/0.4 FOREIGN PATENTS256,105 2/1949 Switzerland 313/178 Primary Examiner-Raymond F. HossfeldAttorney-Hill, Sherman, Meroni, Gross and Simpson ABSTRACT: Anonevaporating getter, which is optionally heatable in operation withinan electron discharge vessel, in whichthe getter material contains atleast one metal selected from the group consisting of Zr, Ta, Hf, Nb,Ti, Th and U, and is disposed directly on the insulating layer of theheating means, eliminating the use of an open metal vessel or the likefor the getter material.

BACKGROUND OF THE INVENTION The invention is directed to a getterstructure for electrical discharge vessels employing a nonevaporablegetter material which contains at least one metal selected from a groupconsisting of Zr, Ta, Hf, Nb, Ti, th and U, which is optionally heatableduring operation of the electrical discharge vessel. ln the past gettersof this type were constructed in the form of an open metal cup orpot-shaped vessel which was associated with an insulated heating coil ofthe type of an indirectly heated cathode with such metal vesselconsisting of the gettering metal or at least provided with a surfacecoating of such metal.

Getters constructed of zirconium, particularly correspondingly thicklayers thereof produced by pressing and sintering of zirconium powderprovide a considerably increased vacuum speed and gas absorptioncapacity at temperatures above 600 C., but at room temperature the gasabsorption capacity is considerably limited by the fact that the gasdiffusion into the interior of the zirconium is eliminated whereby onlythe slight surface absorption of the zirconium layer of the getterremains. However, an increase of the gas absorption capacity of thegetter at room temperature is absolutely necessary to insure maintenanceof the necessary vacuum of larger electronic tubes under storageconditions.

Exhaustive experiments have revealed that an increase of the gasabsorption capacity at room temperature by more than -fold can beachieved with a porous unpressed zirconium body, and in an effort toachieve greater porosity in sintered bodies of zirconium powder forgetter purposes, molybdenum or tungsten powder was admixed with thezirconium powder. This arrangement, however, has the disadvantage, amongothers, that zirconium and molybdenum alloy at l500 C. (2732 F.) as aresult of which the sintering and degasification temperatures of suchoperating electrodes is considerably limited at the upper end.

The present invention therefore has among its objects the elimination ofthe disadvantages associated with getter structures such as thosedescribed and a simple method of producing the same.

BRIEF SUMMARY OF THE INVENTION The present invention proceeds upon theconcept of utilizing carbon in conjunction with the getter material inwhich the sintering of the particles of getter material is partiallyavoided during the heat treatment by employing carbon particles, whichare for example, utilized by mixing carbon powder with the gettermaterial powder and applying the mixture directly to the heating means.By the addition of carbon granules, for example, pressed layers with ahigher porosity can be achieved than with ductile molybdenum ortungsten, and at the same time the gas transfer of carbon granules ismuch lower than that of molybdenum or tungsten powder. Furthermore theporous zirconium-carbon body continues to be readily mechanicallymachinable, even after application of relatively high heat treatmenttemperatures, for example, 1300 C. (2372 F.).

Heatable getters of the type described can also be utilized withparticular advantage in applications where a definite lack of spaceexists in a electron tube, replacing the corresponding heating means,but such arrangement has the disadvantage that the temperature range isfixed at a relatively high level.

In accordance with the method of the invention for producing getters ofthe type described, the heating means, already provided with asintered-on insulation layer, is suitably coated with a powder mixtureof getter metal and carbon and subsequently heat treated in high vacuumat 800l200 C. The powder mixture may be in the form of an alcoholicsuspension and applied by a dipping operation or the dry powder mixturemay be pressed within a pressing die, at low pressure, and the mo dedmaterial subsequently sub ected to the desired heat treatment.

BRIEF DESCRIPTION OF DRAWING The drawing illustrates a vertical sectionthrough a getter structure constructed in accordance with the presentinvention.

DETAILED DESCRIPTION Referring to the figure of the drawing, thereference 'numeral l designates a heating coil, customarily providedwith an insulating coating 2, for example of aluminum oxide, which ifdesired may be of bifilar design. Disposed on the heating coil is a massor body 3 of getter metal and carbon which, after heat treatment in ahigh vacuum, forms a highly porous structure directly on the heatingmeans.

The coating or body 3 may be formed by dipping the heating means in analcoholic suspension of getter metal and up to 30 percent by weightcarbon, particularly electrographite which is thereafter heat treated ina high vacuum at 800- l200 C. until the desired unitary structureresults. This construction provides a very large active getter surfacewhich can be selectively heated as desired during operation by controlof the heating means to provide appropriate temperatures for the desiredapplication.

The coating may be applied by other conventional methods of applicationsuch as atomization or the like. It is also possible to insert theheating means within a die containing a dry powder mixture and by meansof a suitable pressure tool press, with low pressure, a sufficientlythick coating upon the surface of the heating means, thereby embeddingthe latter within the getter material.

A heatable getter structure constructed in accordance with the presentinvention may be disposed in any suitable location within the electrontube associated therewith, completely exposed and positioned at or inthe proximity of the tube electrode system, i.e. wherever there isadequate space to which electrical heating energy can be suppliedthereto. An important advantage of an arrangement in accordance with'the present invention resides in the fact that the structure iscompletely nonmagnetic so that it can be disposed at any suitablelocation in the tube without in any way creating interference withrespect to the electron discharge process of the electron tube involved.

Having thus described my invention it will be obvious that variousimmaterial modifications may be made without departing from the spiritof my invention, hence I do not wish to be understood as limiting myselfto the exact form, construction and arrangement of parts-herein shownand described.

I claim as my invention:

1. The method of making a nonevaporating type of getter, optionallyheatable in operation, having heating means provided with a sintered-onlayer of insulating material, compris ing the steps of mixing carbonpowder with at least one metal powder selected from a group consistingof Zr, Ta, I-If, Nb, Ti, th, and U, with the powder mixture containing'apowder carbon content of up to 30 percent by weight, applying a coatingof such mixture directly to the insulating layer of said heating means,subjecting the coated heating means to a high vacuum, and heating thesame to a temperature of 800-1200" C. while in such vacuum.

2. A method according to claim 1, comprising applying the gettermaterial to the insulating layer of the heating means by dipping thelatter into an alcoholic suspension of getter metal and carbon powders,and thereafter subjecting the same to said heat treatment.

3. A method according to claim 1, wherein a dry powder mixture of gettermetal and carbon is pressed within a pressing die at low pressure toform said coating, and thereafter subjecting the same to said heattreatment.

2. A method according to claim 1, comprising applying the gettermaterial to the insulating layer of the heating means by dipping thelatter into an alcoholic suspension of getter metal and carbon powders,and thereafter subjecting the same to said heat treatment.
 3. A methodaccording to claim 1, wherein a dry powder mixture of getter metal andcarbon is pressed within a pressing die at low pressure to form saidcoating, and thereafter subjecting the same to said heat treatment.